The balls used in various bowling games for a great many years have been made with surfaces which are not absolutely spherical, or else have been weighted in certain ways to cause them to roll in other than straight lines. In bowling with ten pins on wooden alleys, rules have been imposed, to require balls with a truly spherical surface, and to limit the permitted variations in structure, so as to minimize the effects of differences in construction of balls, and enhance the effect of skill in delivery.
Nevertheless, I have found that substantial improvements in bowling scores can be attained by apparently minor modifications of internal structure, within the limits imposed by the rules.
Thus, my prior U.S. Pat. No. 3,865,369 discloses a ball with an internal weight of such a shape that the center of mass of the ball is not at the geometric center but is displaced toward the top where the ball is held by the bowler, and so that a substatial part of the added weight is closer to the surface than to the center so that it exerts a "flywheel" effect on the ball as it rolls. Many bowlers improve their scores by using such a ball.
The ball just described has been found not to be helpful at all to certain bowlers whose delivery is superficially similar to that of the bowlers whose scores have been improved.